Light and adaptive responses in red macroalgae: an overview.

The most recent research shows an increased interest in algal photobiology following the modifications of light spectral composition induced by the 'ozone depletion' in the atmosphere. The consequences of this change on the macrophytic red algae, which possess accessory light-harvesting complexes, are currently uncertain. Moreover the underwater light field of coastal waters, where most macroalgae are living, has been well characterized only in the last few years. The presence and the variability of light components, such as red, far-red, green, blue and ultraviolet radiation, in these environments, at different depths, have raised the question of whether red macroalgae are 'light-intensity or/and light-quality adapters'. In this paper various adaptive responses of red algae, both in the field and under culture, are discussed in order to compare the physiological and ecological results. All these studies seem to suggest that red algae are both 'light-intensity and light-quality adapters'. In particular, the light quality and, overall, the modulation of the ratios between spectral components seem to play the role of photomorphogenic 'signals' regulating algal metabolism and growth. Short- and long-term responses, and potential strategies and mechanisms for adaptation to light at individual, cellular and molecular levels, are discussed with special reference to the photosynthetic equipment.